1. Field of Invention
This invention pertains generally to window systems of the type in which transparency is controlled electrically and, more particularly, to system and method which utilizes a liquid crystal window technology known as xe2x80x9cprivacy glassxe2x80x9d in exterior applications such as windows and skylights.
2. Related Art
Privacy glass is a double xe2x80x9cExe2x80x9d window which, as illustrated in FIGS. 1 and 2, has a liquid crystal film 11 laminated between, two sheets of glass 12, 13. In a non-energized state, the liquid crystal molecules disperse light, but when energized, the liquid crystal molecules are aligned in a manner which permits parallel light to pass through the film.
In its unenergized or natural state, the liquid crystal film is translucent. It has a milky white appearance and essentially prevents objects from being seen through it while still transmitting approximately 70 percent of the light in the visible spectrum. With the application of a small amount of electrical energy, the film becomes optically clear. With 70 percent transmissivity, privacy glass passes substantially more light in its darkened state than other electrochromic windows which pass only about 15-20 percent of the visible light.
For many years, privacy glass has been used in interior applications such as privacy screens for corporate conference rooms and hospital examination rooms, and in recent years, there have been some attempts to utilize privacy glass in the windows of dwellings and other buildings. However, those efforts have generally not been successful because the privacy glass has failed in a relatively short time in exterior applications.
One of the reasons for the rapid failure of windows utilizing privacy glass is the leakage of moisture into the laminated structure. Applicant has found that such leakage can be prevented by good construction techniques such as the use of a proper sealant, e.g. naturally cured silicone, around the edges of the laminated panels, thereby making it feasible to use privacy glass in exterior applications.
U.S. Pat. No. 6,130,772 and the references cited therein disclose additional techniques for controlling the transmissivity of electrochromic windows and other optical elements.
It is in general an object of the invention to provide a new and improved light control system and method.
Another object of the invention is to provide a system and method of the above character which can be utilized in exterior applications such as windows and skylights.
These and other objects are achieved in accordance with the invention by providing a light control system and method in which a privacy glass window having first and second transparent substrates with a film of liquid crystal between the substrates is mounted in the wall or roof of a building. The level of ambient light outside the building is monitored and/or sunlight impinging directly on the building is detected, and the film is energized to make the window transparent during daylight hours when sunlight is not impinging directly upon it. Some embodiments include override switches which permit the window to be made transparent at night and/or during cooler months when sunlight is falling directly on it, and some include an override switch which permits the window to be darkened during daylight hours in warmer months.